Ok, so there are a lot more than just five things that keep people from getting organized. But I thought that we should start with these first. 
Touching papers or things twice
Ok, you finally pick up that pile of paper on the dining room table and realize, after a bit of reading, that it is some supporting tax documents from the previous year. “These papers should be in the tax archives in the basement”, you think to yourself. But instead of going and putting them there or at least near the basement stairwell, labeled, you place the pile back down and decide to do it later. Then some days go by and you want to clear the dining room table off for expected guests, but you have to go through, read and figure out what that pile of paper is all about-again. Wasted mental energy.

Using Post-its Incorrectly
Post-its are one of my favorite organizing “tools”. But too often I see people stick a million and one post-its all over their computer and workspace. Now all those post-its just get lost in their visual field. And sometimes they fall down and sometimes they stick to something else and get lost.Optimal way to use post-its: use them as temporary labels. For example, if you are sorting through lots of papers and files, use a post-it to label the piles, such as, “file under taxes”, “shred”, “pay by Oct. 1”, “archive”, etc.

Not being prepared when starting a new project
Getting ready to start a renovating project, buy a new car, or hire a nanny?Prepare beforehand by having on hand a notebook or a loose-leaf binder (tabbed for very involved projects) to write everything down. Alternatively, you could type notes in a Word Document or an Excel Spreadsheet (OK, now we’re really getting organized.) This is going to be a process, so keep track of contacts, prices, items, stores, websites and/or interview notes. Write clear notes and date everything.

Not labeling stuff
I see clients and others putting stuff in drawers or boxes and counting on that they will remember what it is and where they put it. This is not very likely to happen. Label everything with details. Label makers are fantastic, but it is just as good if you the inexpensive labels from Avery and a good old Sharpie. (Love all the different colors, especially metallic ones!)

Not putting things back in their “homes”
Professional organizers and organized parents review this simple concept of returning things back where you found them–again and again. Create a “home” for every item in your home, in your garage, in your closet, in your drawer, in your desk, in your purse AND then put the item back there after every use. BTW, your choice of a “home” for your item could be totally whacky (e.g. some urban dwellers choose to store clothing in the kitchen)-just be consistent with returning the item to its “home”. This process will almost become mindless. You will never not be able to find something again. BONUS: You will never have to purchase a duplicate of something because you can’t find the original item.